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Search Results: 1 - 10 of 913 matches for " Fatih Vehbi Celebi "
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A Complete CAD Model for Type-I Quantum Cascade Lasers with the use of Artificial Bee Colony Algorithm
Sevgi Yigit,Bulent Tugrul,Fatih Vehbi Celebi
Journal of Artificial Intelligence , 2012,
Abstract: In this study, a simple and a single complete CAD model is obtained for type I quantum cascade laser based on characteristic quantities (optical gain, refractive index change, linewidth enhancement factor). The model is based on Artificial Neural Networks (ANNs) which is optimized by a new algorithm called Artificial Bee Colony (ABC). The developed model is capable of making fast and reliable predictions which is very useful in the CAD design of related systems. The inputs of the model are injection current and wavelength, respectively. The model agrees very well with the experimental findings that are previously published.
Current cardiac imaging techniques for detection of left ventricular mass
Aksuyek S Celebi, Hulya Yalcin, Fatih Yalcin
Cardiovascular Ultrasound , 2010, DOI: 10.1186/1476-7120-8-19
Abstract: Left ventricular hypertrophy (LVH) is an unfavorable condition, which is consistently and strongly associated with significant cardiovascular morbidity and mortality [1]. In addition, left ventricular (LV) mass portends poor patient prognosis independent of traditional risk factors [2]. Furthermore, numerous therapeutic agents are observed to promote LV mass reduction in parallel with improved clinical outcome [3]. As a result, LV mass is suggested as a regular study finding of any cardiac imaging modality [4].LV mass determination by various imaging modalities is principally based on shell volume, which is obtained as the difference of epicardial and endocardial volumes. Shell volume is subsequently converted to mass by multiplying with the specific density of myocardial tissue (usually taken as 1.05 g/mL).Individual variation in body size influences the assessment of LV mass. Indexing is of importance to differentiate between health and disease, to assess the severity of disease, to allow comparisons among varying body size, and to recognize alterations over time. LV mass may be expressed as an index for some variables of body size. The best method for LV mass indexing is still under debate. Different methods of indexation result in considerably different prevalence of LVH [5]. Some investigators have traditionally indexed LV mass to body surface area [6]. However, indexing by body surface area may inappropriately normalize LV mass and must be critically questioned [7]. Normalization for the allometric power of its relation to body height (height2.7 ) provides a greater attributable risk than other methods of indexation [8]. Indexing to height in meters to the power 2.7 successfully facilitates identification of LVH among obese subjects, as well [9]. Nevertheless, lean body mass was found to be more ideal than height and body surface area for indexing LV mass (7). Along with these, identification of LV mass needs to take into account the influence of different eth
Fast Color Space Transformations Using Minimax Approximations
M. Emre Celebi,Hassan Kingravi,Fatih Celiker
Computer Science , 2010, DOI: 10.1049/iet-ipr.2008.0172
Abstract: Color space transformations are frequently used in image processing, graphics, and visualization applications. In many cases, these transformations are complex nonlinear functions, which prohibits their use in time-critical applications. In this paper, we present a new approach called Minimax Approximations for Color-space Transformations (MACT).We demonstrate MACT on three commonly used color space transformations. Extensive experiments on a large and diverse image set and comparisons with well-known multidimensional lookup table interpolation methods show that MACT achieves an excellent balance among four criteria: ease of implementation, memory usage, accuracy, and computational speed.
Time-Delay Estimation in Dispersed Spectrum Cognitive Radio Systems
Kocak Fatih,Celebi Hasari,Gezici Sinan,Qaraqe KhalidA
EURASIP Journal on Advances in Signal Processing , 2010,
Abstract: Time-delay estimation is studied for cognitive radio systems, which facilitate opportunistic use of spectral resources. A two-step approach is proposed to obtain accurate time-delay estimates of signals that occupy multiple dispersed bands simultaneously, with significantly lower computational complexity than the optimal maximum likelihood (ML) estimator. In the first step of the proposed approach, an ML estimator is used for each band of the signal in order to estimate the unknown parameters of the signal occupying that band. Then, in the second step, the estimates from the first step are combined in various ways in order to obtain the final time-delay estimate. The combining techniques that are used in the second step are called optimal combining, signal-to-noise ratio (SNR) combining, selection combining, and equal combining. It is shown that the performance of the optimal combining technique gets very close to the Cramer-Rao lower bound at high SNRs. These combining techniques provide various mechanisms for diversity combining for time-delay estimation and extend the concept of diversity in communications systems to the time-delay estimation problem in cognitive radio systems. Simulation results are presented to evaluate the performance of the proposed estimators and to verify the theoretical analysis.
Time-Delay Estimation in Dispersed Spectrum Cognitive Radio Systems
Fatih Kocak,Hasari Celebi,Sinan Gezici,Khalid A. Qaraqe
EURASIP Journal on Advances in Signal Processing , 2010, DOI: 10.1155/2010/675959
Abstract: Time-delay estimation is studied for cognitive radio systems, which facilitate opportunistic use of spectral resources. A two-step approach is proposed to obtain accurate time-delay estimates of signals that occupy multiple dispersed bands simultaneously, with significantly lower computational complexity than the optimal maximum likelihood (ML) estimator. In the first step of the proposed approach, an ML estimator is used for each band of the signal in order to estimate the unknown parameters of the signal occupying that band. Then, in the second step, the estimates from the first step are combined in various ways in order to obtain the final time-delay estimate. The combining techniques that are used in the second step are called optimal combining, signal-to-noise ratio (SNR) combining, selection combining, and equal combining. It is shown that the performance of the optimal combining technique gets very close to the Cramer-Rao lower bound at high SNRs. These combining techniques provide various mechanisms for diversity combining for time-delay estimation and extend the concept of diversity in communications systems to the time-delay estimation problem in cognitive radio systems. Simulation results are presented to evaluate the performance of the proposed estimators and to verify the theoretical analysis.
Brucellosis in Childhood
Solmaz Celebi,Mustafa Hacimustafaoglu,Fatih Demirtas,Enes Sali
Cocuk Enfeksiyon Dergisi , 2011,
Abstract: Objective: Brucellosis is still an important infectious disease, being widespread as endemic and sporadic cases in Turkey. The aim of this study was to evaluate clinical and laboratory findings, treatment modalities and final outcomes of brucellosis in children. Material and Methods: This is a retrospective record review of all patients 0-18 years of age with brucellosis admitted during a 8-year period between January 2003 and September 2010.Results: Of the 62 patients, 39 (63%) were male. The mean age and standard deviation of patients was 120±51.7 months (4 months-18 years). Most common symptoms on admission were fever (88%), arthralgia (64%) and dizziness (19%). On physical examination, the findings and percentages were as follows; arthritis (29%), lymphadenopathy (25%), hepatomegaly (24%) and splenomegaly (17%). Fifty-one percent of the patients had high sedimentation rate, 41% had high transaminase levels, and 40% had positivity for C-Reactive Protein. Brucella agglutination tests were positive in all cases. Brucella spp. was isolated from blood cultures in 27% of the cases. All of the cases were given combined drug therapy. Three of the cases (4.8%) had relapses during the follow up period. No mortality was seen in patients with brucellosis.Conclusion: Childhood brucellosis remains an important public health problem in our country. It may cause serious complications in children, and treatment with at least two antibiotics for not less than six weeks appears to be effective.
On Euclidean Norm Approximations
M. Emre Celebi,Fatih Celiker,Hassan A. Kingravi
Computer Science , 2010,
Abstract: Euclidean norm calculations arise frequently in scientific and engineering applications. Several approximations for this norm with differing complexity and accuracy have been proposed in the literature. Earlier approaches were based on minimizing the maximum error. Recently, Seol and Cheun proposed an approximation based on minimizing the average error. In this paper, we first examine these approximations in detail, show that they fit into a single mathematical formulation, and compare their average and maximum errors. We then show that the maximum errors given by Seol and Cheun are significantly optimistic.
Cost-Effective Implementation of Order-Statistics Based Vector Filters Using Minimax Approximations
M. Emre Celebi,Hassan A. Kingravi,Rastislav Lukac,Fatih Celiker
Computer Science , 2010, DOI: 10.1364/JOSAA.26.001518
Abstract: Vector operators based on robust order statistics have proved successful in digital multichannel imaging applications, particularly color image filtering and enhancement, in dealing with impulsive noise while preserving edges and fine image details. These operators often have very high computational requirements which limits their use in time-critical applications. This paper introduces techniques to speed up vector filters using the minimax approximation theory. Extensive experiments on a large and diverse set of color images show that proposed approximations achieve an excellent balance among ease of implementation, accuracy, and computational speed.
Comments on "On Approximating Euclidean Metrics by Weighted t-Cost Distances in Arbitrary Dimension"
M. Emre Celebi,Hassan A. Kingravi,Fatih Celiker
Computer Science , 2012, DOI: 10.1016/j.patrec.2012.03.002
Abstract: Mukherjee (Pattern Recognition Letters, vol. 32, pp. 824-831, 2011) recently introduced a class of distance functions called weighted t-cost distances that generalize m-neighbor, octagonal, and t-cost distances. He proved that weighted t-cost distances form a family of metrics and derived an approximation for the Euclidean norm in $\mathbb{Z}^n$. In this note we compare this approximation to two previously proposed Euclidean norm approximations and demonstrate that the empirical average errors given by Mukherjee are significantly optimistic in $\mathbb{R}^n$. We also propose a simple normalization scheme that improves the accuracy of his approximation substantially with respect to both average and maximum relative errors.
Time Delay Estimation in Cognitive Radio Systems
Fatih Kocak,Hasari Celebi,Sinan Gezici,Khalid A. Qaraqe,Huseyin Arslan,H. Vincent Poor
Mathematics , 2009,
Abstract: In cognitive radio systems, secondary users can utilize multiple dispersed bands that are not used by primary users. In this paper, time delay estimation of signals that occupy multiple dispersed bands is studied. First, theoretical limits on time delay estimation are reviewed. Then, two-step time delay estimators that provide trade-offs between computational complexity and performance are investigated. In addition, asymptotic optimality properties of the two-step time delay estimators are discussed. Finally, simulation results are presented to explain the theoretical results.
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